In recent years, the arrival of a new era of information dissemination has required a high operation speed, high integration, and a high mounting density of a semiconductor device. In order to make a semiconductor device operate at a higher speed, it is indispensable to increase the signal propagation velocity on the circuit in addition to shortening the length of the wiring in the device. In this connection, the signal propagation velocity is inversely proportional to the square root of the relative dielectric constant of substrate material. For this reason, substrate material having a lower dielectric constant is becoming necessary. Furthermore, in order to attain the higher integration and the higher packaging density thereof, wiring material having low resistivity (Ag, Au, Cu, and the like) must be used. However, because these metals have a low melting point, it is necessary to use substrate material capable of sintering at a low temperature in the fabrication of a multi-layered printed wiring board that is obtained by sintering the substrate after the wiring pattern was printed thereon. For this reason, an alumina substrate (its dielectric constant: 9 to 9.5, and sintering temperature: approximately 1,500° C.) that has been so far widely used as substrate material for electronic component use are not applicable to high frequency printed circuit boards. Material that is other than this material, namely has a lower dielectric constant and can be sintered at a low temperature is required. In addition, the reduction of loss in a microwave zone and a millimeter-wave zone has been also required of the substrate material.
Therefore, recently, glass ceramic material composed of glass and inorganic filler has been studied for substrate material having a low dielectric constant, which can meet the increase of the operation speed. This type of glass ceramic material is suitable for insulating substrates for high frequency use because of having a low dielectric constant of 3 to 7, and can be advantageously co-sintered with Ag, Au, Cu, and the like each having a low conductor resistance, because the material can be sintered at a temperature of 800 to 1,000° C.
For example, JP-A-2000-188017 (U.S. Pat. No. 6,232,251), discloses a ceramic composition for high frequency use that includes a glass phase capable of precipitating a diopside (CaMgSi2O6) type crystal phase and an oxide containing Mg and/or Zn and Ti as the filler, and that can be sintered at a temperature of 1,000° C. or less. Furthermore, JP-A-2001-240470 discloses a printed wiring board for high frequency use that is composed of a crystallized glass component containing SiO2, Al2O3, MO (M denotes an alkaline earth metal element), and Pb, and at least one type of filler selected from a group of Al2O3, SiO2, MgTiO3, (Mg, Zn) TiO3, TiO2, SrTiO3, MgAl2O4, ZnAl2O4, cordierite, mullite, enstatite, willemite, CaAl2Si2O8, SrAl2Si2O8, (Sr, Ca)Al2Si2O8, and forsterite.
In addition, low temperature sintering ceramic compositions in which boron (B) is used as a sintering aide has been proposed (See JP-A-2002-037661, JP-A-2002-173367, etc.).
However, the above-described glass ceramic material, though having a low dielectric constant, has a high dielectric loss (tanδ) of approximately 2×10−3 or more in a high frequency zone of a signal frequency of 10 GHz or more, that is, substantially in the range of 5×103 to 8×103 in terms of Qf value; accordingly, it does not have the characteristics enough to be put into practical use as the substrate material for high frequency use. For example, the ceramic composition of JP-A-2000-037661 has a Qf value of at most 0.5×103 and the composition of JP-A-2002-173367 has a Qf value on the order of 5×103. Here, the Qf value denotes a product of a measuring frequency (f/GHz) and Q (≅1/tanδ).
Moreover, JP-A-2001-278657 discloses a low temperature sintering ceramic composition that includes a diopside crystal (CaMgSi2O6) phase serving as the main crystal phase, characterized in that the dielectric constant ε of the composition is 7 or less, and the Qf value thereof is 10,000 GHz or more. However, the composition disclosed JP-A-2001-278657 essentially requires being subjected to calcining treatment at 1,100° C. or more, which increases the energy cost and the environmental load when manufacturing the substrate.
For this reason, an object of the present invention is to provide a low temperature sintering ceramic composition that can be co-sintered with a low resistance metal such as Ag, Au, Cu, and the like, reduce the energy cost and the environmental load required when manufacturing the ceramic therefrom, and moreover realize the low dielectric constant and the low dielectric loss in a high frequency region, and to provide a fabricating method of the low temperature sintering ceramic.